1. Field of the Invention
The present invention relates to a semiconductor device containing a plurality of transistors, and more specifically to the structure of the electrode of the semiconductor device.
2. Description of the Related Art
In accordance with the present trend toward smaller electronic equipment, a semiconductor device configured by a smaller module containing a plurality of heat-producing semiconductor elements is demanded.
An existing semiconductor device (power module) is described below by referring to FIGS. 1 and 2. A power module 51 includes a plurality of semiconductor elements. To the bottom of the power module 51, a heat conductive base plate 52 formed by a heat conductive ceramic plate is attached as a heat conductive member.
On the top surface of the heat conductive base plate 52, a substrate 55 and a substrate 56 are provided. The substrate 55 is formed by a conductor layer 55a and an insulating layer 55b, and the insulating layer 55b is in contact with the heat conductive base plate 52. On the other hand, the substrate 56 is formed by a conductor layer 56a and an insulating layer 56b, and the insulating layer 56b is in contact with the heat conductive base plate 52. A plurality of semiconductor elements 57 are provided on the top surface of the conductor layer 55a, and a plurality of semiconductor elements 58 are provided on the top surface of conductor layer 56a. The semiconductor elements 57 and 58 are MOSFETs. A drain of the MOSFET is formed on one surface of each of the semiconductor elements 57 and 58, and a source and a gate are formed on the other surface of the MOSFET. The drain of each semiconductor element 57 is in contact with the conductor layer 55a of the substrate 55, and the drain of each semiconductor element 58 is in contact with the conductor layer 56a of the substrate 56.
A substrate 53 is provided in the central area on the top surface of the heat conductive base plate 52. The substrate 53 is formed by a conductor layer 53a and an insulating layer 53b, and the insulating layer 53b is in contact with the heat conductive base plate 52. A source-drain electrode 54 is connected to the conductor layer 53a. 
The substrates 55, 56, and 53 (and semiconductor elements 57 and 58) are encompassed by a resin case 59. A drain electrode 60, a source electrode 61, and gate electrodes 62 and 63 are attached to the resin case 59. The resin case 59 is fixed to the heat conductive base plate 52.
As shown in FIGS. 1 and 2, wire bonding connects the drain electrode 60 with the conductor layer 55a of the substrate 55, the source of each semiconductor element 57 with the conductor layer 53a of the substrate 53, the conductor layer 53a with the conductor layer 56a of the substrate 56, the source of the semiconductor element 58 with the source electrode 61, the gate of the semiconductor element 57 with the gate electrode 62, and the gate of each semiconductor element 58 with the gate electrode 63.
In this semiconductor device, if the substrates 53, 55, and 56 are made small, then a smaller power module can be produced. However, it is necessary for the substrate 53 to reserve an area for wire bonding and an area for the source-drain electrode 54. In addition, it is necessary to increase the number of the semiconductor elements 57 and 58 in order to increase the capacity of the power module 51, thereby also requiring larger substrates 55 and 56. As a result, there has been a lower limit for the size of the substrates 53, 55, and 56. That is, it has not been easy to realize a smaller semiconductor device such as a power module, etc.
The present invention aims at downsizing a semiconductor power module including a plurality of semiconductor elements.
The semiconductor device according to the present invention includes a plurality of semiconductor elements, a case provided as encompassing the plurality of semiconductor elements, and an electrode which is incorporated into the case for the main current of the semiconductor elements. These components are arranged such that the electrode bridges over the area of the semiconductor elements when the case is fixed in a predetermined position for the semiconductor elements.
According to this structure, the semiconductor elements (or their circuits) can be provided under the electrode. Therefore, a smaller semiconductor device can be realized. In addition, since the electrode is incorporated into the case, the assembly task for the semiconductor device can be simpler.
This semiconductor device can be configured such that the terminals for electric connection between the semiconductor device and the circuits outside the semiconductor device can also be incorporated into the electrode. With the configuration, since it is not necessary to connect the electrode to the terminals, the assembly task for the semiconductor device can be yet simpler.
This semiconductor device can also be configured such that the electrode can be connected to the semiconductor elements through wire bonding. With the configuration, the space in the case can be efficiently utilized.
This semiconductor device can be configured such that the electrode can directly or indirectly contact the metal contact surface provided in a predetermined position for the semiconductor elements so that the metal contact surface is connected to the semiconductor elements through the wire bonding. With the configuration, the wire can be applied before fixing the case, thereby realizing an easier bonding operation.
Furthermore, this semiconductor device can also be configured such that partitioning members for sectioning the area inside the case can be provided at the bottom portion of the electrode. With the configuration, a gel, if it is filled inside the case, can be protected against shaking. As a result, an excess tension on the wire can be avoided.